High-temperature lubricating grease



Patented Jan. 1, 1952 HIGH -TEMPERATURE LUBRICATING' GREASE Arnold J. Morway,

Rahway, and John J. Kolfenbach, Somerville, N. 5., assignors to Standard Oil Development Company, a corporation of Delaware No Drawing. Application January 25', I950,

Serial No. 140,546

12 Claims.

The present invention relates to hightemperature lubricating greases and especially to greases which contain complex salt and soap thickeners as distinguished from the simple soap type thickeners commonly used in the prior art. The invention also includes, as one aspect, a new process for producing grease compositions of the type refererd to above. The products of this invention have very good structural stability and resistance to oxidation and for this reason they are useful for long and severe service, as in antifriction bearings which are infrequently lubricated.

It has been suggested previously that grease thickeners in which low molecular weight salts of various organic acids are combined or complexed with conventional soaps have certain advantages over the conventional soaps alone. In general, such greases may be used at higher temperatures because of higher dropping points and their structural stability at more usual temperatures often is improved considerably. Among useful acids previously suggested are acetic, propionic, acrylic, crotonic, glycolic, lactic and furoic acids. On the other hand, caproic acid, which is of slightly higher molecular weight, has been found unsatisfactory.

According to the present invention, metal salts, particularly the alkali metal and alkaline-earth metal salts, of alpha keto aliphatic acids having not more than 7- ca-rbon atoms, may be combined advantageously with conventional soaps to make greases. Other metal saltsthan the alkali and alkaline earth metals may be used in some cases, e. g., lead, zinc, and even aluminum salts, but those first mentioned are preferred. The sodium salts are preferred, but lithium and calcium make good products. In general, proportions of l to 2 parts by weight of low molecular weight salts to 1 to 10 parts of conventional soaps may be used. By the expression conventional soaps it is intended to cover the usual metal soaps of fatty acids of about 12 to 24. carbon atoms, the alkali and alkaline earth metal soaps, specifically sodium, lithium, calcium and barium soaps, and mixture of any of these, being preferred, but other metals such as lead, zinc and aluminum appear to be useful in some cases. These soaps and salts are, of course, used in suitable lubricating oils, especially mineral base oils and sometimes in other conventional oils, to thicken them to grease consistency.

The low molecular weight acids used in forming the greases of the present invention are typified by pyruvic acid which has the formula v be used provided Immediate homologs of this acid, and their isomers and closely related acids, may likewise they do not have more than carbon atoms. It isnecessary carbonyl group have the posicarboxyl group, as in pyruvic acid. Thus, the beta keto acid, acetoacetic acid (CHcCOCHzCOOH) and its salts are very unstable and cannot be used. Its next higher homolog, the gamma keto acid, levulinic acid (CI-IsCOCI-IzCHzCOOH), is more stable but is unsatisfactory as a grease constituent. It was earlier supposed that the ketonic linkage of levuiinic acid was the cause of its failure but that does not now appear to betrue since alpha keto acids are satisfactory. The failure of this acid is no doubt due to the relatively remote position of the carbonyl group from the carboxyl group. In general, the useful acids are of formula where R is an aliphatic hydrocarbon group of 1 to 5 carbon atoms, preferably but not necessarily saturated, and the carbonyl group is adjacent the carboxyl group. Alpha keto acids containing a total of 3 to 4 carbon atoms, for ex'- ample pyruvic acid, are specifically preferred. Other acids which may be used are the following: Propionyl formic acid, butyryl formic acid, dimethyl pyroracemic acid, trimethyl pyroracemic acid, and isobutyryl formic acid;

The preferred process for making these greases includes the steps of making a concentrate of the soap and salt in mineral oil of lubricating grease, using 25% to of the total oil to be employed, cooking this concentrate sufficiently to remove all moisture, e. g., to a temperature of F., and finally working in the remainder of the oil at a higher temperature, cooking to about 400 F. to 500 F., and then cooling, homogenizing and packaging.

The invention will be more fully understood by reference to the following specific example:

Example I A grease composition was prepared from the following ingredients:

about '7 aliphatic that the keto or F. The pyruvic'acid was next tion, was added immediately thereafter. Mixin and heating were continued until a temperature of about 275 F. was reached. During such heating, the soap and salt were formed and water was evaporated. The product at this stage was dry and of heavy consistency. Thereafter, the remainder of the mineral oil was mixed in, with stirring, being gradually worked into the heavy concentrate. Heating was continued during addition of this mineral oil and thereafter until a final cooking temperature of 450 F. was reached. At this stage, the antioxidant, phenyl alpha naphthylamine, was added and mixed in and the grease was then cooled. Cooling may be accomplished either in the kettle, accompanied by continuous working, or in conventional cooling pans. After cooling, the grease was homogenized by milling. A Cornell or equivalent homogenizer may be used for this homogenization.

The product of the example had the following properties:

Consistency-unworked 210 min/l penetraon. Consistency after 60 strokes in standard 240 mm./10.

grease worker.

Obviously, greases may be varied in their constituents by using larger or smaller quantities of salt and/or soap, by using mixtures of soaps or by using the salt of one metal and the soap of another or several other metals. Preformed soaps may be used, if desired, which are incorporated in at least part of the oil before the saltforming constituents are added or at least before the basic components are added. The total soap content of the finished grease will ordinarily be between and 35% by weight, to 25% being preferred. The salt content should be 2 to 10%, preferably about 3 to 6 or 7%. The total thickener content thus is about 7 to 45%, 13% to about 32% being preferred. The proportions of Example I appear to be about optimum for average uses.

Conventional modifiers such as antioxidants, extreme pressure additives, tackiness agents, metal deactivators, and the like, may be used. It is preferred to use at least a small amount, from 0.2 to 2% and usually about 0.5 to 1% by weight, based on the total composition, of a good oxidation inhibitor such as phenyl alpha or phenyl beta naphthylamine, but even this can be dispensed with in some cases.

While mineral base oils are preferred as the major liquid constituent of the grease, the synthetic oils such as the alkyl esters of polybasic acids or the polyglycol and polyether types may be used in part or in whole. It is usually preferred to form the soaps and salts in situ and in this case a neutral and chemically inert oil, preferably mineral oil, should be used for preparing the soap-salt concentrate. However, the soap and salt may both be preformed, in which case they may be added as such directly to synthetic oils. This ordinarily requires intensive dispersion and for this reason the method set forth in Example I, using mineral oil at least for the concentrate, is usually the most convenient and satisfactory.

While the sodium salt-soap concentrate of Example I is a highly satisfactory thickener for high temperature lubricating greases, good grease products may be made by using lithium bases, or calcium, barium, strontium, zinc, lead and aluminum bases, singly or in various combinations. The sodium base product is ordinarily preferred, calcium being next in utility and lithium being well suited for some applications.

What is claimed is:

1. A lubricating grease composition comprising a lubricating oil thickened to grease consistency with 1 to 2 parts by weight of a metal salt of a low molecular weight acid and 1 to 10 parts of a metal soap of fatty acids having between 12 and 24 carbon atoms per molecule, said low molecular weight acid having the general formula R--COCOOH where R is an aliphatic hydrocarbon group of 1 to 5 carbon atoms.

2. Composition according to claim 1 wherein the metal salt is an alkali metal salt.

3. Composition according to claim 1 wherein the metal salt is an alkaline earth metal salt.

4. Composition according to claim 1 wherein the metals of the salt and soap are identical.

5. Composition according to claim 1 wherein the metals of the salt and soap are sodium.

6. Composition according to claim 1 wherein the low molecular weight acid is pyruvic acid.

7. A lubricating grease composition comprising a lubricating oil thickened to a grease consistency with 2 to 10% by weight, based on the total composition, of a metal salt of an alpha keto carboxylic aliphatic acid having not more than 7 carbon atoms combined with 5 to 35% of a metal soap of fatty acid having between 12 and 24 carbon atoms per molecule.

8. Composition according to claim 7 having a salt content of 3% to 7% and a soap content of 10% to 25%.

9. A lubricating grease composition consisting essentially of about 72 parts by weight of mineral base lubricating oil thickened to a grease consistency with a complex metal salt and soap comprised of the reaction product of 4 parts pyruvic acid, 17 parts fatty acid of between 12 and 24 carbon atoms and 5.4 parts sodium hydroxide, plus about 1 part antioxidant.

10. The process of preparing a lubricatin grease which comprises preparing in one-fourth to one-half the lubricating oil to be used a concentrated complex of l to 2 parts by weight of metal salt of a C3 to C1 alpha keto aliphatic carboxylic acid with 1 to 10 parts of the corresponding metal soap of fatty acids having between 12 and 24 carbon atoms per molecule, heating with working to a temperature within the range of 250 F. to 300 F., adding further oil and working while the cooking temperature is gradually increased to a range between 400 F. and 500 F., and thereafter cooling and homogenizing.

11. Process according to claim 10 wherein the metal of the soap and salt is sodium.

12. Process according to claim 10 wherein the keto acid is pyruvic acid.

ARNOLD J. MORWAY. JOHN J. KOLFENBACH.

REFERENCES CITED The following references are of record in the file of this patent:

I UNITED STATES PATENTS 

1. A LUBRICATING GREASE COMPOSITION COMPRISING A LUBRICATING OIL THICKENED TO GREASE CONSISTENCY WITH 1 TO 2 PARTS BY WEIGHT OF A METAL SALT OF A LOW MOLECULAR WEIGHT ACID AND 1 TO 10 PARTS OF A METAL SOAP OF FATTY ACIDS HAVING BETWEEN 12 AND 24 CARBON ATOMS PER MOLECULE, SAID LOW MOLECULAR WEIGHT ACID HAVING THE GENERAL FORMULA 